Keysight DAQ970A User Guide

Where:
Vs = Ideal DUT voltage
Rs = DUT source resistance
Ri = Input resistance (10 MΩ or >10 GΩ)
To minimize loading errors, set the DMM's DC input resistance to greater than 10 GΩ when needed.
Loading Errors Due to Input Bias Current
The semiconductor devices used in the input circuits of the internal DMM have slight leakage currents
called bias currents. The effect of the input bias current is a loading error at the internal DMM’s input ter-
minals. The leakage current will approximately double for every 10 °C temperature rise, thus making the
problem much more apparent at higher temperatures.
Where:
I
b
= DMMbias current
R
s
= DUTsource resistance
R
i
= Input resistance (10 MΩ or >10 GΩ)
C
i
= DMMinput capacitance
Error (V) = I
b
× R
s
AC Voltage Measurements
The main purpose of an AC “front end” is to change an AC voltage input into a DC voltage which can be
measured by the ADC.
Signal Conditioning for AC Measurements
Keysight DAQ970A User's Guide 197
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Keysight DAQ970A Specifications

General

Scan Rate	Up to 450 channels/sec
Connectivity	USB, LAN, GPIB (optional)
Display	4.3-inch color LCD
Operating Temperature	0 °C to 50 °C
Number of slots	3 slots
Measurement Types	DCV, ACV, DCI, ACI, 2-wire resistance, 4-wire resistance, frequency, temperature, capacitance
Voltmeter	6.5 digit
Resolution	22 bits
Memory	Non-volatile memory